Sex identification is important in bird breeding and conservation. However, birds of many families are sexually monomorphic, rendering it difficult to identify their sex via appearance.
Genetic variances have been found between the chromo-helicase-DNA-binding protein 1 (CHD1) gene located on W chromosome (the female bird-specific sex chromosome) and its counterpart located on Z chromosome (the mutual sex chromosome of both male and female birds). More specifically, two CHD1 introns exhibit length differences between their W and Z counterparts. See Fridolfsson et al., 1999; Kahn et al., 1998; and Griffiths et al., 1998. These intron length differences were utilized to determine the sex of some non-ratite birds. See Griffiths et al. 1998; and Jensen et al. 2003. This approach, however, is not applicable to birds in many families, e.g., Strigidae, as the length differences are indiscernible in these families. See Kahn et al., 1998; and Fridolfsson and Ellegren 1999.
Thus, there is a need to develop a new sex-determining method that is applicable to a large number of bird families.